More Ribbon Mic Question

[cettelbrick]

I've done a lot of searching around in here and haven't really found the answer I am looking for.

Anyone experiencing good results from a Chinese Ribbon direct into an interface? I was experimenting with a Firewire 410 and the Ribbon mic got very noisy (air sounds) at the highest gain levels.

Just wondering what results others were having.
What preamps are you using with Chinese Ribbons?

 

[scrubs]

It's not the mic that is getting noisy, most likely, but the preamp. Ribbon mics have essentially no self noise. For high gain sources, like guitar amps, you might be able to get away with cheap, noisy preamps, as you won't require as much gain from the pre. However, for softer sources, you need a preamp with more clean gain. On the budget end, the Studio Projects VTB-1 has +72 dB of available gain and is pretty quiet up until the last click or 2. It also has variable input impedance, which is nice for ribbons. Other budget choices would be the M-Audio DMP3 and Rane MS1B, both of which have around +65dB of relatively clean gain.

Higher end options like the AEA TRP (The Ribbon Preamp) would also be great.

 

[Marik]

Ribbon mics have essentially no self noise.

In fact they do and come from the resistance of the primary of the transformer together with the DCR of the ribbon itself. It is stepped up by the transformer's secondary and if the ribbon (or primary) have a high DCR, the noise can be pretty significant, among other things.

 

[Obi-Wan zenabI]

My RSM-4 is making em happy enough recording jazz vox and tenor sax, right into my firepod. Thru my V4's, I'm not hearing anything really noticeable as far as noise. There's not a lot of high end extension to the sound, but it works for what I am tracking.

I'm happier with the voice than the tenor sound, well, at least my tenor player doesn't like it so much, but I like how it sits in the mix and it seems to take eq well. Or rather, my inexperienced use of EQ doesn't seem to turn it into a turd, which happens with some of my other cheap mics sometimes.

OWz

 

[crazydoc]

In fact they do and come from the resistance of the primary of the transformer together with the DCR of the ribbon itself. It is stepped up by the transformer's secondary and if the ribbon (or primary) have a high DCR, the noise can be pretty significant, among other things.

How many milliohms are we talking about here, both for ribbon and transformer? I've seen transformer specs for primaries from the 50 to 400 range. I can't imagine a 2" by 1/4" aluminum ribbon having even that much resistance.

 

[Chris Long]

My humble Audio Buddy seems to work just fine with the ribbons I got (ACM 1 and 3). No noticeable noise when the gain is cranked high. And it is able to provide enough to drive the ribbons (I think it's listed as +66dBs, tops)

 

[Marik]

How many milliohms are we talking about here, both for ribbon and transformer? I've seen transformer specs for primaries from the 50 to 400 range. I can't imagine a 2" by 1/4" aluminum ribbon having even that much resistance.

If the pri. is in 50 Ohm then it is definitely not for a ribbon. The mic will be hissing like crazy even at 1/10th of that. The Lundahl with all primaries in parallel gives about 0.05 Ohm. Even this can be considered slightly on the higher side. I use different techniques for winding transformers and get under 0.01 Ohm.

The DCR of the ribbon itself has range between something like 0.05 to 1 Ohm depending on its thickness. Ironicly, the benefit of having 6um ribbon many Chinese are using, is that in fact, it has low self noise .

Best, M

 

[crazydoc]

If the pri. is in 50 Ohm then it is definitely not for a ribbon. The mic will be hissing like crazy even at 1/10th of that. The Lundahl with all primaries in parallel gives about 0.05 Ohm. Even this can be considered slightly on the higher side. I use different techniques for winding transformers and get under 0.01 Ohm.

The DCR of the ribbon itself has range between something like 0.05 to 1 Ohm depending on its thickness. Ironicly, the benefit of having 6um ribbon many Chinese are using, is that in fact, it has low self noise .

Best, M

Sorry to be confusing - I was talking about milli-ohms, so transformer primaries would be in the 0.05 ohm to 0.40 ohm range.

So you're saying that the ribbon itself can have a DCR up to 1 ohm? It just seems high to me. I'll have to look at the resistivity and cross sectional area and calculate it.

 

[mshilarious]

Check my math here:

If we use 0.1 ohms as the DCR, that is thermal noise across a 20kHz bandwidth of -165dBV. That might be more bandwidth than relevant to a ribbon mic, but it's only a few dB different.

Anyway, if we get 40dB? of gain from the transformer that's -125dBV, in reference to 1 Pa at -55dBV (just to make the math easy ), that's 70dB of dynamic range, unweighted. A-weighted would improve that maybe 6dB, so let's say 18dBA self-noise? That seems really high. I must be off somewhere . . .

 

[Marik]

Check my math here:

If we use 0.1 ohms as the DCR, that is thermal noise across a 20kHz bandwidth of -165dBV. That might be more bandwidth than relevant to a ribbon mic, but it's only a few dB different.

Anyway, if we get 40dB? of gain from the transformer that's -125dBV, in reference to 1 Pa at -55dBV (just to make the math easy ), that's 70dB of dynamic range, unweighted. A-weighted would improve that maybe 6dB, so let's say 18dBA self-noise? That seems really high. I must be off somewhere . . .

You are asking me for math... in the evening, after dinner with wine?

OK,

Let's get there from the other side.

To get your 0.1 ohms let's say we've got 0.05 Ohm of the ribbon itself and 0.05 ohm primary. Let's assume the secondary is 100 Ohm and we have a 1:40 transformer loaded into "standard" 1.5K.
Then the noise figure of increased impedance is
20Log of sqrt of (realZout) 221 Ohm/(IdealZout) 75.94 Ohm=4.6db

I am way too lazy to calculate series losses level drop, but since the resistances are not that high I'd say 1 db would be about right for total noise figure about 5.6 db... unless I am drunk and completely wrong

But wait a second, that's only how much noise the ribbon and transformer contribute together. To get the dynamic range we need to take into account way too many things--efficiency of the system, area and mass of the ribbon, front to back path length, etc. Definitely not a task for tonight...

Best, M

 

[crazydoc]

So you're saying that the ribbon itself can have a DCR up to 1 ohm? It just seems high to me. I'll have to look at the resistivity and cross sectional area and calculate it.

A ribbon 0.5 cm wide, 5 cm long and 2 um thick, with a resistivity of aluminum of of 2.65*10^-8 ohm.m, would have a DCR of 0.135 ohms. A 6 micron ribbon would be 0.037 ohms. So 0.05 ohms is in the ballpark, but 1 ohm is too high.

Carry on.

 

[Marik]

A ribbon 0.5 cm wide, 5 cm long and 2 um thick, with a resistivity of aluminum of of 2.65*10^-8 ohm.m, would have a DCR of 0.135 ohms. A 6 micron ribbon would be 0.037 ohms. So 0.05 ohms is in the ballpark, but 1 ohm is too high.

Carry on.

Have you ever seen a double 2" 0.6um ribbon?

 

[fova]

I am using T-Bone RB100 (the same as Nady RSM 3) through german preamp SPL Goldmike ( http://www.spl-usa.com/GoldMike/in_detail.html )

To get the same level of signal from ribbon like I usually get from condensers I have to set gain on Goldmike to 75%.
In this position of gain there is an audiable noise but it is not anything terrible and a record can be used in mix.

Goldmike is a hybrid - solid state/tube where the signal first goes thru a solid state circuit, then it is colored by tube. In my opinion it is a middle class preamp.

It is definitelly critical to have a "clean" preamp with a low self noise for recording of ribbons.
I think solid states such as DMP 3 can do a good job here.

 

[Shadow_7]

From what I've gathered of many ribbon mic specs, you need at least +55dB of low noise gain. And many ribbon mics do NOT play well with Phantom Power. In fact using PP can damage ribbon mics. If you are having gain issues you might try a Rode D-Plug. +20dB between the ribbon and preamp.

You should also factor in your cables, since you are pushing your preamps gain so high. The high impedence of some preamps is specifically to overcome degredation through long cable runs. Many of the high end gear specs to about 10K of impedence or higher. The AEA TRP is something like 18K of impedence. As opposed to the Art Tube MP (2K), or DMP3 (3K), or MPA Gold (variable 0.15K-3K).

 

[fova]

I am not using phantom power for ribbon.

These are parameters of my equipment:

SPL Goldmike

Signal to Noise Ratio: -85.6 dBu (A-weighted) at 30 dB Gain
Input Impedance: 1.8 kOhm
Output Impedance (XLR/Jack): < 600 Ohm

Microphone cables are 5 meter long Sommer Cable Galileo ( http://www.sommercable.com/2__default/index.html ) with these parameters:

Construction (2LI2Y0.38mm2)YDDY
Jacket, diameter PVC 7,0 mm
AWG 21
No. of inner conductors 2 x 0,38 mm2
Copper strand per conductor 48 x 0,10 mm
Conductor insulation PE 1,55 mm
Shielding double copper spiral, counter-rotating
Shielding factor 100 %
Temperature range min. -30 °C
max. 70 °C
Fire load per m 0,22 kWh
Weight per 1 m 60 g
Packaging 100 m roll
Capac. cond./cond. per 1 m 50 pF
Capac. cond./shield. per 1 m 100 pF
Cond. resistance per 1 km < 52 Ohm
Shield. resistance per 1 km 25 Ohm
Insulation resist. per 1 km > 1 GOhm
Surge impedance 38 Ohm

What do you think?

 

[mshilarious]

You should also factor in your cables, since you are pushing your preamps gain so high. The high impedence of some preamps is specifically to overcome degredation through long cable runs. Many of the high end gear specs to about 10K of impedence or higher. The AEA TRP is something like 18K of impedence. As opposed to the Art Tube MP (2K), or DMP3 (3K), or MPA Gold (variable 0.15K-3K).

You can safely ignore cables for studio use (and pretty much for live use too, unless you have a REALLY long run). What matters for cable capacitance is source impedance, not load impedance. Both are low enough--let's say 100pF/m for debate, in a 10m cable that's 1nF, with a source impedance of 300 ohms that's a -3dB corner over 500kHz (not really correct as the source impedance at 500kHz is presumably higher than nominal, but we don't really care about that). In fact we could safely go to 100m and still not affect audio measurably.

At that 100m you'd have 10 ohms resistance per the specs above, also trivial in comparison with any likely load impedance.

I'm not sure why AEA spec'ed 18K load impedance; a higher load impedance would let you use a higher source impedance, which would mean a higher ratio transformer and more gain before the noise of the preamp. But then you'd have that higher source impedance, and perhaps you would start to become concerned about cable losses at some point. I don't know that AEA makes such a mic, but maybe they are thinking about it.

The most important spec of the AEA pre is self-noise, at -130dB (doesn't say weighted or unweighted at their site). That's the problem with the Rode D-Plug: high self-noise, -116dBA. So if you're looking for more gain, and your preamp is quieter than that (a semi-decent one should be), I'd just do a digital gain change.

Oh, I noticed a funny typo at the AEA site: "-3 dB at 300 kH". Without that "z" on the end, it would be Henries, not Hertz. It's nonsensical, but it's funny to think about a 300,000 H inductor

 

[mshilarious]

You are asking me for math... in the evening, after dinner with wine?

But wait a second, that's only how much noise the ribbon and transformer contribute together. To get the dynamic range we need to take into account way too many things--efficiency of the system, area and mass of the ribbon, front to back path length, etc. Definitely not a task for tonight...

Best, M

Yeah I think if I messed something up, it was the wild guess at sensitivity. If the typical figure I picked doesn't line up with the assumption about transformer ratio, that's a big error right there.

 

[Shadow_7]

and the Ribbon mic got very noisy (air sounds) at the highest gain levels.

I guess it depends on what you call air sounds. Ribbon mics are sensitive to gusts of air. And should not be used for things like kick drums. Or even guitar amps, in close proximity anyway. Probably not that great for use outdoors either.

Now if you're just referencing the humm / buzz / hiss of the noise of your preamp/converter. Then that's why your higher end preamps run $2,000 and up. Also, solid state electronics tend to be a bit noisier than Tubes. Although tubes don't take abuse, or age very well.

Many of the combined converters and preamps tend to be lower end gear. And when pushed at the last quarter turn of the gain knob, will have a noticeable change in signal to noise ratio. Or not, you could have a damaged mic. What are you recording anyway? flute from across a large room? Trumpet from inches away? Ambient room noise?

You might try recording with the gain knob at 75% and then digitally boosting the loudness of the recorded track. If that has a noticeable difference in noise ratio to having the gain knob towards 100%, then it's probably the preamp and not the mic. Not that chinese ribbons are renowned for their quality and consistency.

 

[chance]

I am using T-Bone RB100 (the same as Nady RSM 3) through german preamp SPL Goldmike ( http://www.spl-usa.com/GoldMike/in_detail.html )

How do you like the SPL gold mike ? What is the cost of this animal ?

 

[cettelbrick]

Thanks for all the replies. I played around with some other gear I had lying about and got some pretty good levels and sounds, so I'm sure it is just the 410 preamp. It is always interesting to see what other people are playing around with though.